In the diverse multisystem and multistandard wireless communication environment, software-defined radio is an extremely promising technology. Wide-band code-division multiple access (CDMA) has been promoted for International Mobile Telecommunications year 2000 (IMT-2000) third-generation wireless systems (3G) primarily because of its greater capacity compared with time-division multiple access (TDMA) and frequency-division multiple access (FDMA) systems for cellular communication. However, the performance of wideband CDMA suffers from multiple access interference (MAI) and inter-symbol interference (ISI) due to severe multipath fading. To combat the hostile wireless channel and meanwhile better utilize the spectrum and radio resources with acceptable bit error rates (BER), CDMA combining orthogonal frequency-division multiplexing (OFDM) has been proposed for future wireless multimedia communications.
Many experts believe that multimedia communication will be in the main stream of future communications systems, but it generates problems in effective transmission. As code-division multiple-access (CDMA) is being utilized for the third generation and other possible future communication systems due to its advantages over other multiple access schemes, there is a need to actuate multimedia services based on CDMA. On the other hand, orthogonal-frequency-division-multiplexing (OFDM) has been used in high-speed digital communications, which can be efficiently implemented by the Fast-Fourier-Transform (FFT) digital technique (K. Fazel, S. Kaiser and M. Schnell, “A flexible and high-performance cellular mobile communication system based on orthogonal multi-carrier SSMA,” IEEE Wireless Personal Communications, vol. 2, No. 1, pp. 121–144, 1995), and is known as an approach to the problems inherent in highly hostile mobile channels in high-speed transmissions. Combining CDMA and OFDM results in a finer partition of radio resources, which makes the resource allocation more effective. Therefore, OFDM-CDMA for multimedia applications is an attractive candidate for Fourth Generation wireless communication systems (4G). The realization of multi-rate transmission and implementation by a flexible software-defined architecture is of significant interest. Generally, multiple access schemes based on the combination of CDMA and OFDM can be divided into three types, namely MC-CDMA, MC-DS-CDMA, and MT-CDMA (Shinsuke Hara, Rarnjee Prasad, “Overview of multicarrier CDMA,” IEEE Communication Magazine, pp. 126–133, December 1997). However, these prior art designs are only suitable for use in single rate data streams, and are not suitable for use in multi-rate applications.